Spraying method and apparatus

ABSTRACT

A method for spraying an aqueous liquid into the air intake duct ( 2 ) of a turbocharged piston engine ( 1 ) for humidifying the intake air to reduce nitrogen oxide emissions. In a first stage in the method, the intake air is heated by a heat exchanger element ( 5 ′) before the turbocharger and water midst is injected into the air intake duct after the first heading stage through at least one first nozzle ( 9, 10 ), and in a second stage the intake air is compressed by the turbocharger ( 4 ), causing its temperature to rise, and water mist is injected into the air intake duct through at least one second nozzle ( 12, 13 ) after the second stage.

BACKGROUND OF THE INVENTION

The present invention relates to a method as defined in the preamble ofclaim 1 for spraying an aqueous liquid into the air intake duct of aturbocharged piston engine for humidifying the intake air to reducenitrogen oxide emissions.

The invention also relates to a spraying apparatus as defined in claim 3for humidifying the intake air of a turbocharged piston engine to reducenitrogen oxide emissions, said apparatus comprising at least one nozzlefor spraying an aqueous liquid into the air intake duct.

The invention thus concerns especially a method and apparatus forsupplying water into the intake air of a turbocharged piston engine toreduce nitrogen oxide emissions (NOx). At the high combustiontemperatures, the combustion process in the cylinder of a piston engineproduces nitrogen oxides, which are emitted together with the exhaustgases into the atmosphere. Because of the harmful climatic effects ofnitrogen oxide emissions, efforts are undertaken to minimize theirproduction.

As is known, adding water to the combustion process in the form ofeither water vapor or water droplets reduces the generation of nitrogenoxides. This phenomenon is based on a cooling effect. When the watersprayed into the cylinder is evaporated, it reduces the temperature ofthe air in the cylinder while at the same time reducing the pressure.The pressure drop has an adverse effect on the efficiency, although thedecrease of pressure and temperature has a favorable effect on theformation of nitrogen oxides. When the water is supplied in the form ofdroplets together with the intake air, some of it is additionally wastedduring the scavenging period and water consumption is increased. Whenair saturated with water vapor is supplied into the cylinder, thethermal capacity of the filling gas is increased and the gas has asubstantially greater effect of reducing the temperatures of thecombustion process than does dry air. The effect of reducing thecombustion temperatures increases with the water vapor concentration,yet without producing an undesirable effect on efficiency. Since anincrease in the temperature of the gas supplied into the cylinder alsoaugments the generation of nitrogen oxides as well as the consumption ofwater, it is desirable to keep the gas temperature as low as possible,yet high enough to ensure that the gas supplied into the cylindercontains an amount of water vapor sufficient for the reduction ofnitrogen oxides.

An apparatus for vaporizing a desired amount of water is disclosed inpatents U.S. Pat. No. 5,758,606 and U.S. Pat. No. 6,196,165. A drawbackwith this apparatus is that the device mounted between the turbochargerand the cylinder increases the cubic volume of the air intake ductwork,which has a considerable effect on the power output of the engine. Thepower output is dependent on the cubic volume after the turbochargerbecause during power increase or decrease the air pressure produced bythe turbocharger increases the density of the air and the amount of gasentering the cylinder. If the cubic volume between the turbocharger andthe cylinder is increased, it will take considerably longer before theamount of air produced by the turbocharger brings the pressure to thedesired level and the power generated by the engine increases. Anotherdrawback with the apparatus is that the heated water used forvaporization and flushed over the evaporation surfaces has the effect ofincreasing the temperature of the air. The device is unable to make useof the cooling effect produced in connection with the vaporization ofthe water, but the gas output from the device is at a relatively hightemperature, so the amount of water vapor required for the reduction ofnitrogen oxides and therefore also the water consumption are increasedconsiderably.

Specification WO98/10185 again discloses an apparatus in which the airproduced by a turbocharger and the pressure of this air are utilized inthe injection of water for humidifying the air supplied to theturbocharger. A drawback with this system is the relatively lowtemperature of the supply air, which is why the amount of water vaporevaporated into the air remains small, and thus no significant nitrogenoxide reducing effect is achieved. Another drawback is that when theamount of water is increased, the water droplets can evaporate after theair has reached a saturated state, with the result that the waterdroplets drift into the turbocharger and cause wear of the turbochargervanes through droplet erosion. From a thermodynamical viewpoint, thedrifting of droplets into the turbocharger is desirable as it reducesthe work performed by the turbocharger, increasing the pressure of thepressurized air produced at the output and simultaneously reducing itstemperature. In practice, however, a turbocharger rotating at a veryhigh speed—about 50,000-100,000 rpm—has proved to be very sensitive todroplet erosion as referred to above.

The object of the present invention is to achieve a spraying system forsupplying water mist into the air intake ductwork of especially a pistonengine and allowing the drawbacks of prior-art to be avoided. Anadditional object of the invention is to achieve a method and apparatusthat will enable efficient humidification of intake air.

The method of the invention is mainly characterized in that, in a firststage in the method, the intake air is heated by a heat exchangerelement before the turbocharger and water mist is injected into the airintake duct after the first heating stage through at least one firstnozzle, that in a second stage the intake air is compressed by theturbocharger, causing its temperature to rise, and water mist isinjected into the air intake duct through at least one second nozzleafter the second stage.

The apparatus of the invention is mainly characterized in that theapparatus comprises at least one heating element for heating the intakeair before the turbocharger and at least one first nozzle for injectingan aqueous liquid mist into the air intake duct after the heatingelement.

The apparatus of the invention is further characterized by what isstated in claims 4-10.

The solution of the invention has numerous significant advantages. Theapparatus is connected directly to the structures of the air intake ductand it produces a fine mist directly without using any extra chambers orother containers, it is able to make full use of the heat quantityrequired for the vaporization of the water, cooling the intake air ateach spray injection point to a temperature close to the wet bulbtemperature (or adiabatic saturation temperature, which in the case of awater-air mixture is practically the same thing), i.e. to thetemperature to which the air temperature can be reduced by vaporizationof water. As connecting the apparatus of the invention to a turbochargedengine does not involve any changes in the cubic volume of the airintake system, it has no adverse effect on the power output of theengine, either.

By the method of the invention, very good and efficient humidificationof intake air is achieved. The heating of intake air used in the methodcan be implemented using a relatively economic construction as it doesnot have to withstand the high pressure after the turbocharger. Theefficiency of the turbocharger is increased because the mass flowpassing through it is larger than before. In addition, the engine'sresponse time for power boost is accelerated because the turbochargerduct volume is reduced.

Another advantage of the apparatus of the invention is that the humidityof the intake air can be increased stepwise after each heat supplypoint, yet before the last heat supply point, which can be used as awater evaporation surface, thus controlling the humidity of the gas fedinto the cylinder and therefore the formation of nitrogen oxides withindesired limits.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in detail by the aidof an example with reference to the attached drawing, wherein

FIG. 1 presents diagram representing an apparatus according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a diagrammatic representation of a apparatus according to theinvention, installed in connection with the air intake duct 2 of apiston engine, such as a diesel engine. The air intake duct 2 and theexhaust gas duct 3 are shown in a simplified form in the FIGURE. Theengine presented in the FIGURE is provided with a turbocharger 4, whichfeeds air under positive pressure into the air intake ductwork 2 of theengine. To reduce the nitrogen oxide emissions of the engine, the airintake ductwork is provided with at least one spraying head 6, 7 fittedto supply water mist into the intake ductwork 2. Turbocharged enginesare traditionally provided with a charge-air intercooler 5, which in theFIGURE is depicted in broken lines.

According to the invention, the intake air is heated by means of a heatexchanger element 5′, such as an intake air intercooler relocated to theappropriate position and converted to function as a heater as well, e.g.by providing it with equipment for engine HT-water circulation. Afterthe first heating stage, aqueous liquid mist is sprayed into the intakeair, causing the intake air temperature to fall due to the evaporationcooling of the aqueous liquid and the intake air mass flow to increase.In the next stage, an intake air compressor, such as a turbocharger 4,compresses the air, thereby raising its temperature. In a second stageafter the compressor, aqueous liquid mist is injected into the intakeair, with the result that the intake air temperature falls and at thesame time the best evaporation result in respect of the overall outcomeis achieved.

Method of the invention for spraying an aqueous liquid into the airintake duct 2 of a turbocharged piston engine 1 for humidifying theintake air to reduce nitrogen oxide emissions. In the method, the intakeair is heated in a first stage before the turbocharger by a heatexchanger element 5′ and water mist is injected into the air intake ductafter the first heating stage through at least one first nozzle 9, 10,and in a second stage the intake air is compressed by the intake aircompressor 4, causing its temperature to rise, and water mist isinjected into the air intake duct through at least one second nozzle 12,13 after the second stage. The amount of water supplied through thenozzles is adjusted according to the load and/or rotational speed of theengine.

Spraying apparatus for humidifying the intake air of a turbochargedpiston engine 1 to reduce nitrogen oxide emissions, said apparatuscomprising at least one nozzle for spraying an aqueous liquid into theair intake duct 2. The apparatus comprises at least one heating element5′ for heating the intake air before the turbocharger 4 and at least onefirst nozzle 9, 10 for injecting an aqueous liquid mist into the airintake duct after the heating element 5′. The apparatus comprises atleast one second nozzle 12, 13 for injecting aqueous liquid mist intothe air intake duct 2 after the compressor 4. The apparatus comprisesvalve elements 13, 14 used to control and/or to open/close the liquidflow passage leading to the nozzles 9-13. At least one first intake airheating element 5′ is a heat exchanger element. At least one seconddevice heating the intake air is the intake air compressor 4. Theapparatus comprises control equipment by means of which the sprayingaction of at least some of the nozzles 9-13 can be controlled.

By the method of the invention, very good and efficient humidificationof intake air is achieved. The heating of intake air used in the methodcan be implemented using a relatively economic construction as it doesnot have to withstand the high pressure after the turbocharger. Theefficiency of the turbocharger is increased because the mass flowpassing through it is larger than before. In addition, the engine'sresponse time for power boost is accelerated because the turbochargerduct volume is reduced.

At least one nozzle of the spraying apparatus is connected directly tothe structures of the air intake duct 2 and it produces a fine mistthrough its spraying head 6, 7 comprising at least one nozzle directlyinto the intake air in the air intake duct. When the solution of theinvention is used, no extra chambers or other containers are need to beprovided in the air intake duct. The nozzles feed a water mist into theair intake duct at a high pressure. The apparatus comprises means forproducing the required amount of water to the desired pressure and toachieve a droplet size as favorable as possible. The pressure in theliquid supply piping is typically over 10 bar, preferably over 30 bar,most preferably over 50 bar. The pressure may be typically between10-300 bar. The liquid, especially aqueous liquid injected into the airintake ductwork is a fine mist. Typically, 90% of the water volume(Dv50) is in the form of droplets typically having a droplet size below200 micrometers, preferably below 100 micrometers and more preferablybelow 50 micrometers. Under high load conditions, the droplet size maybe larger.

The system comprises means for supplying an aqueous liquid to thenozzles. In the embodiment presented in FIG. 1, the system comprises aliquid source 21, from where the liquid is pumped through a pipe 17 bymeans of a pump 15. The pump is operated by a drive 16. The pump istypically a high pressure pump, e.g. a displacement pump. The liquid canbe directed via channels 18, 19 to different nozzles. It is alsopossible to supply different mediums to the nozzle, such as water andgas. The FIGURE does not show the nozzles in detail, but they may bereplaceable depending on the application. The nozzles are therefore of atype such that they produce a spray of fine mist when supplied withliquid under a high pressure. Many kinds of nozzles of this category areknown, e.g. from fire extinguishing technology employing water mist. Forexample, specifications WO 92/20454 and WO 94/06567 disclose nozzlesthat produce a water mist at a high pressure. Naturally, other types ofnozzles may also be used, e.g. specification WO 01/45799 discloses yetanother nozzle.

The amount of water supplied through the nozzles typically increaseswith increasing engine load. Thus, when the engine load is low, it ispossible to supply water only to some of the nozzles and increase thenumber of nozzles spraying when the load increases. Similarly, thespraying head can be provided with nozzles having different properties,such as flow rate, droplet size produced by the nozzles, etc. It is thuspossible to form different combinations which can be adapted to a widerange of different applications, different engine types, differentplacements and conditions.

Typically, the amount of water supplied through the nozzles increaseswhen the engine load increases. This can be implemented e.g. by using acontrol system whereby the speed of rotation of the pump 16 is increasedby the drive device driving the pump. This increases the pressure in thesupply piping 17 and, based on data provided by a pressure transmitter,liquid flow passages 18, 19 are opened for more nozzles 9-13 and/or anozzle having a greater spraying capacity is engaged by opening a liquidflow passage for it. Similarly, when the load decreases, the liquid flowpassages are closed for some of the nozzles and/or a nozzle with a lowerspraying capacity is engaged. Correspondingly, an arrangement can beused such that, when the load is low, liquid is injected from nozzlesproducing a smaller droplet size, and when the load increases, thedroplet size is increased, e.g. by opening a liquid flow passage tonozzles producing larger droplets.

The apparatus of the invention is able to make full use of the heatquantity required for the vaporization of the water, cooling the intakeair at each spray injection point to a temperature close to the wet bulbtemperature (or adiabatic saturation temperature, which in the case of awater-air mixture is practically the same thing), i.e. to thetemperature to which the air temperature can be reduced by vaporizationof water.

In the method and apparatus of the invention, the humidity of the intakeair is preferably increased stepwise after each heat supply point. Inthe direction of the intake air flow, water mist is injected before thelast heat supply point, which can advantageously be used as a waterevaporation surface. By this arrangement, the humidity of the gas fedinto the cylinder and therefore the formation of nitrogen oxides isregulated within the desired limits.

The apparatus comprises a system required for the control of the amountof water to be injected, by means of which the amount of water to beevaporated into the intake air and the cooling of the intake air can becontrolled. The apparatus comprises valve elements 13, 14 arranged inconnection with the liquid flow passages leading to the nozzles, e.g. inconnection with the pipes 18, 19. The valves 13, 14 are typicallycontrolled by a control system 20, allowing the liquid flow passages 18,19 to be opened and closed as necessary.

It is obvious to the person skilled in the art that the invention is notlimited to the embodiments described above, but that it may be variedwithin the scope of the claims presented below.

1. Method for spraying an aqueous liquid into the air intake duct (2) ofa turbocharged piston engine (1) for humidifying the intake air toreduce nitrogen oxide emissions, characterized in that, in a first stagein the method, the intake air is heated by a heat exchanger element (5′)before the turbocharger and water mist is injected into the air intakeduct after the first heating stage through at least one first nozzle(9,10), that in a second stage the intake air is compressed by theturbocharger (4), causing its temperature to rise, and water mist isinjected into the air intake duct through at least one second nozzle(12, 13) after the second stage.
 2. Method according to claim 1,characterized in that the amount of water supplied by the nozzles isadjusted according to the load and/or speed of rotation of the engine.3. Spraying apparatus for humidifying the intake air of a turbochargedpiston engine (1) to reduce nitrogen oxide emnissions, said apparatuscomprising at least one nozzle for spraying an aqueous liquid into theair intake duct (2), characterized in that the apparatus comprises atleast one heating element (5′) for heating the intake air before theturbocharger (4) and at least one first nozzle (9,10) for spraying anaqueous liquid mist into the air intake duct after the heating element(5′).
 4. Spraying apparatus according to claim 3, characterized in thatthe apparatus comprises at least one second nozzle (12,13) for sprayingan aqueous liquid mist into the air intake duct (2) after theturbocharger (4).
 5. Spraying apparatus according to claim 3,characterized in that the apparatus comprises valve elements (13,14)used to control and/or to open/close the liquid flow passage leading tothe nozzles (9-13).
 6. Spraying apparatus according to claim 3,characterized in that at least one first intake air heating element (5′)is a heat exchanger element.
 7. Spraying apparatus according to claim 3,characterized in that at least one second device heating the intake airis an intake air compressor (4).
 8. Spraying apparatus according toclaim 3, characterized in that the apparatus comprises control equipmentby means of which the spraying action of at least some of the nozzles(9-12) can be controlled.
 9. Spraying apparatus according to claim 3,characterized in that the droplet size of the liquid mist is usuallybelow 200 micrometers.
 10. Spraying apparatus according to claim 3,characterized in that the pressure in the liquid supply piping is 10-300bar.